Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae) Author Perkins, Philip D. text Zootaxa 2021 2021-06-28 4994 1 1 93 journal article 10.11646/zootaxa.4994.1.1 1175-5326 5043261 107FCA64-345F-40A4-99D3-5C1441EEAD93 Hydrochus xingu , new species Figs. 3 , 46 , 57 , 70 Type Material. Holotype (male): “ BRAZIL : Para ; Rio Xingu Camp , ( 3°39’S , 52°22’W ), Altamira (ca. 60km S.), 15 Oct. 1986 , P. Spangler & O. Flint // Colln. #24 pond at 2nd palm grove on trail 1” ( NMNH ) . Paratypes (50): Same data as holotype (22 NMNH ) ; Rio Xingu Camp , Altamira (ca 60km S.), 1st jungle stream on trail 4, colln. #6, ( 3°39’S , 52°22’W ), 3.x.1986 , leg. P. J. Spangler & O. S. Flint (1 NMNH ) ; Rio Xingu Camp , Altamira (ca 60km S.), pond at 2nd palm grove on trail 1, colln. #20, ( 3°39’S , 52°22’W ), 11.x.1986 , leg. P. J. Spangler & O. S. Flint (4 NMNH ) ; same locality, 12.x.1986 , leg. P. J. Spangler & O. S. Flint (20) (22 NMNH ) ; Rio Xingu Camp , Altamira (ca. 60km S.), ( 3°39’S , 52°22’W ), 1.x.1986 , leg. P. Spangler & O. Flint (1 NMNH ) ; Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.49 mm ), the black to bronze dorsal color, the pronotum with shallow impressions and dense, rather uniform punctuation, the elytral interstriae narrow ridges, often forming zig-zag pattern, the pronotal shape, and the male genitalia ( Fig. 46 ; described below). Differentiation from other similarly small sized species with similarly shaped pronotum will require dissection of males. Description . Size: holotype (length/width, mm): body (length to elytral apices) 2.49/0.94; head width 0.64; pronotum l/w 0.62/0.66; PA 0.62; PB 0.54; elytra 1.61/0.94. Habitus as illustrated ( Fig. 46 ). Dorsum black to grey to bronze, with very slight iridescence, elytra with black spots. Legs brown. Dorsal punctuation dense. Punctation on elytra ca. 2x that of pronotum. Elytra interstriae narrow ridges, often forming zig-zag pattern, to ca. 0.5x strial puncture diameter, or less. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th very weakly raised, if at all. Pronotum length less than width (ratio ca. 33/35), densely coarsely punctate, of quite uniform puncture size; widest at anterior margin, narrowed at base, sides weakly sinuate, smooth; anterior margin slightly bisinuate; depressions shallow. Elytra with spaces between strial punctures narrow walls to ca. 0.5x their diameter; apices slightly produced, separately rounded in dorsal view, in lateral view outer margin without angulation. Ventral characters: Mentum punctate, with central depression; submentum without foveae. Male genitalia ( Fig. 46 ) general characters: genitalia without parameres; basal piece elongate, nearly straight in both dorsal/ventral and lateral views, basal 3/5 thickened, markedly arcuate in lateral view, distal ½ thin, apex bifid, distal piece issuing from between bifurcations; distal piece elongate, in lateral view very slightly sinuate, decreasing slightly in width from base to apex, apex slightly widened and bearing minute tapering process, in dorsal/ventral views very gradually decreasing in width from base to apex, apex truncate; basal piece/distal piece length ratio ca. 50/11. Etymology . Named in reference to the geographical distribution. New Distribution Records